Field of the Disclosure
The present disclosure relates generally to providing adaptive synthetic positioning when a portable device with a Global Navigational Satellite System (GNSS) receiver is in a blocked area and, more specifically, to calculating and storing parameters in a portable device which can be used to model the travel path through a blocked area (such as, e.g., a tunnel) and improve position solutions when exiting the blocked area.
Description of the Related Art
Satellite navigational systems provide positional and sometimes time information to earth-bound receivers. Each system has its own constellation of satellites, sometimes referred to as satellite/space vehicles (SVs), orbiting the Earth, and in order to calculate its position a receiver in that system on Earth uses the satellites “in view” (i.e., in the sky above) of that system's constellation. Generally, the larger the number of satellites in view, the more accurate the calculation of the receiver's position is likely to be. Global Navigational Satellite Systems (GNSS) is often used as the generic term for such systems, even though such navigational satellite systems include regional and augmented systems—i.e., systems that are not truly “global.”
As the electronics for GNSS receivers have gotten smaller, and the positional calculations have become more accurate, the use of GNSS functions has become ubiquitous in consumer and other electronic devices, from cellular telephones to automobiles. As the number of uses for GNSS receivers has grown substantially and is still growing, the number of GNSS systems, both planned and presently operational, is also growing. The widely-known, widely-used, and truly global Global Positioning System (GPS) has been joined by one other global system, the GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and is currently being joined by the Galileo and BeiDou systems—each of which has, or will have, its own constellation of satellites orbiting the globe. The rise in truly global GNSSs is resulting in a new generation of “multi-constellation” GNSS receivers which receive signals from more than one satellite constellation (e.g., two or more of GPS, Galileo, GLONASS, and/or BeiDou) and can provide much greater accuracy because the number of unblocked satellites overhead at any time from several constellations is always greater than the number of SVs overhead from a single constellation. The term “GNSS receiver” as used herein is not limited to any particular kind or type of GNSS receiver, and of course includes multi-constellation receivers, single constellation receivers, augmented system receivers, receivers with multiple positioning systems, etc.
Regional satellite navigational systems (those that are not global, but intended to cover only a certain region of the globe) include the Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigational Satellite System (IRNSS) currently being developed. Augmented systems (which are normally regional as well, and which “augment” with, e.g., messages from ground-based stations and/or additional navigational aids) include Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Multi-functional Satellite Augmentation System (MSAS), and GPS Aided Geo Augmented Navigation (GAGAN). The term “GNSS,” as used herein, covers any type of navigational satellite system, whether global, regional, augmented, or otherwise, unless expressly indicated otherwise.
Broadly speaking, the reception/processing of GNSS signals involves three phases: acquisition, tracking, and positional calculation (producing a “navigation solution” or “position solution”). Acquisition is the acquiring or identifying of the current satellites in view (SVs), which means satellites that are “visible” overhead, i.e., the satellites from which the GNSS receiver can receive signals. Obviously, in any truly “global” GNSS constellation of satellites, only some of the satellites are orbiting overhead at any time. Acquisition might use one or more of satellite almanac and/or ephemeris information, the GNSS receiver's last positional calculation, assistive information concerning the local region received by terrestrial transmission, signal processing (specifically, finding satellite signals by correlating known signal patterns, such as pseudorandom sequences), and other means well-known by those of ordinary skill in the art, in order to acquire the current SVs. Acquisition can be understood as “finding” the SVs, and tracking as the fine tuning of the signals received from the acquired SVs and keeping track of the acquired SVs over time. Once acquired and adequately tracked, the SV's signals are processed to extract the navigational, positional, timing, and other data transmitted in each SV's signal, and the data from all the SV's being tracked is then used to calculate the GNSS receiver's position. Of course, there are further complexities to the actual reception and processing of GNSS signals, such as various loops feeding back information between these phases for further correction and adjustment of data, as is known to one of ordinary skill in the art.
However, there are times when all of the satellites overhead are completely blocked and/or their signals fail to reach the GNSS receiver, such as when travelling through a tunnel. Various solutions have been proposed for operating a GNSS receiver while in a blocked area, also referred to as being “offline” or in a “dead zone”.
Accordingly, there is a need for methods, systems, and portable devices capable of adaptive synthetic positioning while in a dead zone, with a minimum drain on available resources (both hardware and software) and less required complex calculations/interactions.